This recently came up when I was talking to a customer, they weren't aware that you had to take care of the leather watch strap. But you definitely have too.
Leather is just like your skin, so if you don't condition it then it will crack, and it will start to harden.
Due to the fact that it does not receive nourishment like your skin does. So it is up to you to take care of it. But the key is to not wait until your oils/sweat soaked into. Start right when you get that leather product. That way you ensure it has some longevity to it.
How to look after your leather watch strap
There are a ton of products out there that you can use. Just remember that when you condition it the leather will darken some.
Here is a picture of a ToxicROO N8O after conditioning it, and wearing it for about 3 weeks.
Enjoy your strap. If you ever have a question then please let us know.